How to generate a Boolean (0|1) randomly given the probability of the truth event in C?

Question

I am trying to create a function for a larger problem, and only the function has the following description: returns a non-null integer with probability f, and returns 0 with probability 1 f, where 0 f 1

My code is at this point, but I think I’ve mixed concepts and I don’t even know what I’m doing anymore. How to fix?

int sorteia_voto_com_falha (double f);
    int i, N;

    srand(RAND_MAX);
    for(i = 1; i < N; i++)
       return(rand() % 1-f);

In main() the person enters the number of votes N, and the statement basically says that each vote that a person receives, has probability f to be accounted for with failure for the opposite candidate.

Link to the statement

Answer 1

The function rand() returns a value between 0 and RAND_MAX.

This variable is set in the file stdlib.h.

And they’re outfitted in a break:

_____________________________________
| | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | |
-------------------------------------
0    ^      RAND_MAX/2           RAND_MAX
     |
     5% estão abaixo desse número

Its function HouveFalha(double probabilidade) must be something like:

int HouveFalha(double probabilidade)
{
  return ( ( (double)rand() / (double)RAND_MAX ) < probabilidade ) ? 1 : 0;
}

Don’t forget to initialize a seed with srand():

srand(time(NULL));

link to IME

Ternary operator

The operator ? used in the code is a ternary operator, it is called ternary because it receives three operands.

In functional language would be the equivalent:

?(condition, truth, false)

In Agaric notation (the one used in programming language) it is used as follows:

condition ? truth : false

that line is equivalent to:

if(condition) { Truth Return; } Else { fake Return }

From writing so much this code someone invented this shortcut.

In that case the condição is:

( ( (double)rand() / (double)RAND_MAX ) < probabilidade )

The seed of the GNA Random Number Generator (RNG)

Rand() generates pseudo-random numbers, i.e.:

• They are generated mathematically with some account

• The seed is used to initialize the algorithm.

• Can be equipped in an interval.

• Given the same seed, the same sequence will be generated.

• Not suitable for encryption/security.

• Useful in everyday Monte Carlo simulations.

To create a randomness in the seed, the current time is used as seed, it is not mandatory, but it is a common practice:

srand(time(NULL));